Fire (Gemstone Term)
Also called dispersion
Fire is the rainbow coloured flash a diamond throws when white light splits into its separate colours inside the stone. Gemmologists call the effect dispersion. It is separate from brilliance, which is the plain white light a stone reflects back.
Where the colours come from
White light is made of every colour mixed together. When it enters a stone it bends, and each colour bends by a slightly different amount, so they fan out and leave the stone at different angles. What reaches your eye is a flash of one colour at a time.
How much a material does this varies. Moissanite disperses light more strongly than diamond, which is why it shows more coloured flash, and some buyers read that extra fire as a giveaway.
Showing fire in a render
Fire only appears when a light source is small and bright and the stone is moving. A flat studio light gives you brilliance but almost no colour flash, which is one reason a still image can make a good stone look ordinary.
We light stones with sources shaped to bring out the coloured flashes, and the 3 videos delivered with every file are where fire actually shows, because the stone turns and the colours change as it goes.
Questions about Fire
What is the difference between fire and brilliance?
Fire is coloured flash from light splitting inside the stone. Brilliance is the white light bounced straight back. A good stone shows both.
Can a photo show a diamond's fire?
Only partly. Fire depends on movement and on small bright light sources, so video shows it far better than a single still image.